Sediment samples from Antarctica reveal million-year-old DNA

Remains of these marine microorganisms were discovered around 178 m deep in ocean floor sediments in Antarctica.

Representational image: Studying the past and present responses of the polar marine ecosystem to environmental change is a matter of urgency. | Photo Credit: The Hind

The DNA of ancient microorganisms estimated to be around a million years old have recently been found in the seafloor of the Scotia Sea near Antarctica. 

Remains of marine microorganisms were discovered around 178 m deep in the sediments of the ocean floor in Antarctica during an expedition in 2019. The samples are the oldest authenticated DNA to be discovered till date. Previously, the oldest DNA ever found was 6,50,000 years old, buried within sub-arctic permafrost deposits.

Dubbed sedimentary ancient DNA or sedaDNA, this DNA comes from eukaryotes—organisms whose cells contain a nucleus and membrane-bound organelles. The group of scientists that conducted the study are unsure of the species of these organisms as eukaryotes include animals, plants, fungi and algae. 

“The fragments are the oldest authenticated marine  sedaDNA discovered to date – and these have been preserved due to factors like very low temperatures and oxygen concentrations, and an absence of UV radiation,” said Dr Linda Armbrecht, a researcher at the Institute for Marine and Antarctic Studies and lead author of the study. 

The study, published in Nature Communications, analysed the fragmented DNA samples using a new technique called sedaDNA analysis which helped the scientists understand “what has lived in the oceans” through the various ice-age cycles Earth has experienced.

Scientists identified a variety of microorganisms apart from the million-year-old eukaryote, such as 5,40,000-year-old chlorophytes and diatoms—photosynthesising algae found in aquatic and moist environments.

Around 14,500 years ago, the Earth was warming naturally after an ice age. Warmer waters and rising sea levels due to the melting of the ice sheet contributed to the rapid growth of diatoms in the oceans, the paper noted. 

“This interesting and important change is associated with a world-wide and rapid increase in sea levels and massive loss of ice in Antarctica due to natural warming – warming that apparently caused an increase in ocean productivity around Antarctica at that time,” said Dr Michael Weber, a co-author of the study. 

Various species of the tiny diatoms still exist in our oceans and form the base of the food chain as they are primary food sources for larger organisms.

Discovery and analysis of the sedaDNA in Antarctica has ensured that scientists can get a peek into the rhythms of the oceans over hundreds and thousands of years. They can explore the effects of the multiple glacial-interglacial cycles on the Earth’s ecosystems and predict the outcomes of climate change in polar regions more accurately.

“Antarctica is one of the most vulnerable regions to climate change on Earth and studying the past and present responses of this polar marine ecosystem to environmental change is a matter of urgency,” the paper stated.

• The DNA of ancient microorganisms estimated to be around a million years old have recently been found in the seafloor of the Scotia Sea near Antarctica
• Remains of marine microorganisms were discovered around 178 m deep in the sediments of the ocean floor in Antarctica during an expedition in 2019
• Scientists identified a variety of microorganisms apart from the million-year-old eukaryote, such as 5,40,000-year-old chlorophytes and diatoms—photosynthesizing algae found in aquatic and moist environments